Spiro derivatives of formula (I) are particularly useful intermediates in the manufacture of certain cyclic ketones, eminently interesting in the perfumery field. Examples of these cyclic ketones include cis-jasmone, methyl jasmonate and methyl dihydrojasmonate, whose olfactive properties of flowery, jasmin-like character have gained an increased acceptance in the art. Not surprisingly therefore, the scientific literature is rich in articles reporting processes for their preparation [see e.g.: Parfums, cosmetiques et savons de France, 2,356(1972); Synth. Commun., 4, 265(1974); Parfums, cosmetiques et aromes 1975, [4] 33 and ditto, 1976 [12] 53; Tetr. Letters, 1976, 4867 and the references cited therein].
G. Descotes et al. [Synthesis 1974, 118] have described a process for the preparation of cis-jasmone which process consists in converting a cis-vinyl spiranic ketone into its corresponding cis-diene derivative via the reaction pathway illustrated by the following reaction scheme. ##STR3##
Though original from the scientific viewpoint, the method illustrated above presents serious practical and economical drawbacks, namely in consideration of the cost of certain of the reactants used and of the number of reaction steps actually required. Consequently, the above described method is unsuitable for the large scale industrial manufacture of jasmone.
The process of the present invention is relatively simple procedurally and high yields of the intermediate spiroderivatives of formula (I), and consequently of cis-jasmone, as well as parent derivatives such as methyl jasmonate, are obtained in a rather economic way by making use of cheap commercially available reagents.